1. Field of the Invention
This invention relates to a semiconductor device in which semiconductor thin films carry out a photoelectric conversion of incident light, so as to generate an electric power.
The semiconductor device of the type referred to can be effectively utilized in optical control circuits and the like.
2. Description of the Related Art
Hitherto, there have been suggested various types of the semiconductor devices of the kind referred to as being applicable to optical control circuits.
For example, the present inventors have already disclosed in earlier U.S. Pat. No. 4,916,323 a switching device comprising semiconductor devices formed as an array of photoelectric conversion elements and connected to the gate of a field effect transistor (which shall be referred to as "FET" hereinafter) or the like as a switching element. This switching device also includes a light emitting element, the light from which element is received by the array of the photoelectric conversion elements to generate electric power, and the FET or the like is caused by this electric power to perform a switching operation. In order that, in this case, the FET or the like as a voltage controlled element is driven, it is normally required that a plurality of the photoelectric conversion elements be connected in series to generate a voltage exceeding a threshold voltage across the source and gate of the FET or the like. For the series connection of these photoelectric conversion elements, they are to be first formed respectively in an island shape as mutually separated elements and then connected to each other through a conductive thin film. According to the arrangement of this earlier invention, there can be attained various advantages, e.g., the switching device can be provided at a lower cost and higher in utility than when the photoelectric conversion elements are formed on the respective separated islands on a dielectric isolation substrate as has been earlier practiced, if an array of the photoelectric conversion elements can be formed directly on a semiconductor substrate on which FET's and the like are formed so as to allow the device to be formed from one chip, and so on.
Further, in U.S. Pat. No. 4,400,221, there is disclosed an arrangement which permits a photovoltaic force to be generated by a solar battery with a light emitting diode used as a light source. Further, U.S. Pat. No. 4,320,247 discloses a semiconductor device comprising a lamination of seven pn layers.
In the semiconductor devices of the kind referred to, on the other hand, there has been a tendency that, while generally a thicker semiconductive film causes incident light to be sufficiently absorbed but charge carriers are collected insufficiently, a thinner semiconductive film causes the carrier collection to be sufficient but the light absorption to be insufficient, and it has been thus required to optimally combine the sensitivity of the semiconductor device with the wavelength of light from the light emitting element so as to attain a high photoelectric conversion efficiency. However, this requirement has not been sufficiently realized by the foregoing prior art.